Despite being used in clinical practice for several decades, levodopa (L-DOPA) continues to be the gold standard drug for the symptomatic treatment of Parkinson's disease. This has helped to maintain keen interest in the development of inhibitors of the enzyme catechol-O-methyltransferase (COMT) based on the hypothesis that inhibition of this enzyme may provide clinical improvements in patients afflicted by diseases such as Parkinson's disease and undergoing treatment with L-DOPA and a peripheral amino acid decarboxylase (AADC) inhibitor.
The rationale for the use of COMT inhibitors as adjuncts to L-DOPA/AADC therapy is based on their ability to reduce metabolic O-methylation of L-DOPA to 3-O-methyl-L-DOPA (3-OMD). The duration of L-DOPA induced clinical improvement is brief as a result of the short in vivo half-life of L-DOPA which contrasts with the long half-life of 3-OMD. Additionally, 3-OMD competes with L-DOPA for transport across the blood-brain barrier (BBB), which means that only a very limited amount of an orally administered dose of L-DOPA actually reaches the site of action, i.e. the brain. Commonly, within only a few years of starting L-DOPA therapy with the usual dosage regime, L-DOPA induced clinical improvement declines at the end of each dose cycle, giving rise to the so-called ‘wearing-off’ pattern of motor fluctuations. A close relationship between the ‘wearing-off’ phenomenon and accumulation of 3-OMD has been described (Tohgi, H., et al., Neurosci. Letters, 132:19-22, 1992). It has been speculated that this may result from impaired brain penetration of L-DOPA due to competition for the transport system across the BBB with 3-OMD (Reches, A. et al., Neurology, 32:887-888, 1982) or more simply that there is less L-DOPA available to reach the brain (Nutt, J. G., Fellman, J. H., Clin. Neuropharmacol., 7:35-49, 1984). In effect, COMT inhibition protects L-DOPA from metabolic breakdown in the periphery through O-methylation, such that with repeated doses of L-DOPA, the mean plasma L-DOPA concentration is raised. In addition to reduced competition for transport into the brain, a significantly greater percentage of the orally administered dose of L-DOPA is able to reach the site of action. Thus, COMT inhibition serves to increase the bioavailability of L-DOPA and therefore the duration of antiparkinsonian action is prolonged with single doses of L-DOPA (Nutt, J. G., Lancet, 351:1221-1222, 1998).
5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol is a COMT inhibitor exhibiting an exceptionally long duration of action as well as balanced properties of bioactivity, bioavailability and safety. It markedly enhances the bioavailability of L-DOPA, increases the delivery of L-DOPA to the brain and significantly augments the levels of dopamine in the brain over extended periods of time.
As such, 5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol is a promising candidate for treating a subject afflicted by a central or peripheral nervous system disorder, in particular for treating mood disorders, movement disorders such as Parkinson's disease and parkinsonian disorders and restless leg syndrome, gastrointestinal disturbances, oedema formation states and hypertension.
Methods of preparing 5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol are described in WO2007/013830 A1.
The ability of a substance, for example 5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol, to exist in more than one crystalline form is defined as polymorphism and these different crystalline forms may be referred to as “polymorphic modifications” or “polymorphs”. For the purposes of this specification, the term ‘polymorph’ may also encompass pseudo-polymorphs. In general, polymorphism is caused by the ability of the molecule of a substance to change its conformation or to form different intermolecular and intramolecular interactions, particularly hydrogen bonds, resulting in different atomic arrangements in the crystal lattices of the different polymorphs. The polymorphs of a substance possess different crystal lattice energies and, thus, also exhibit different solid state physical properties such as morphology, density, melting point, colour, stability, dissolution rate, milling facility, granulation properties, compacting properties etc.
There are a number of processes for characterizing polymorphs. State of the art technologies include X-ray-based technologies such as X-ray powder diffraction, single crystal X-ray diffraction, microscopy, differential scanning calorimetry, and spectroscopic methods such as IR, near-IR (NIR), Raman and solid state NMR.
In pharmaceutical compositions, the use of different polymorphs often influences factors such as the preparation of pharmaceutical compositions, their stability, dissolution properties, bioavailability and, consequently, their action. In other words, the use of polymorphs allows modulation of the performance of an active pharmaceutical ingredient (API) such as 5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxa-diazol-5-yl]-3-nitrobenzene-1,2-diol as well as affecting the formulation of the API.
Accordingly, it is the object of the present invention to provide novel polymorphs of 5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol.